Digital signal processing has been proven to be very efficient in handling and manipulating large quantities of data. There are many products that are in common use such as wireless devices, digital cameras, motor controllers, automobiles, and toys, to name a few, that rely on digital signal processing to operate. Many of these products continuously receive information such as light intensity, temperature, revolutions per minute, air pressure, and power, for example, which is monitored and used to produce adjustments to the system, thereby maintaining optimum performance. This monitored information is often in the form of an analog signal that must be converted to a representative digital signal. An analog-to-digital converter (ADC) is used to convert the analog signal to the digital signal. In general, the analog-to-digital conversion process comprises periodically sampling the analog signal and converting each sampled signal to a corresponding digital signal.
Many products require ADCs to have the capability of handling both single ended rail-to-rail inputs (e.g., a single signal representing a voltage) and differential rail-to-rail inputs (e.g., complementary signals representing the same voltage). Also, due to pin limitations, the reference voltage used by the ADC may be derived from a main power supply (e.g., VDDA, VSSA). To satisfy these requirements, existing ADCs contain a separate configurable block that scales and converts the voltage and reference inputs to the desired differential levels and then provides the scaled analog input voltage to a redundant signed digit (RSD) analog-to-digital converter stage to perform an initial residue calculation operation. The presence of this separate scaling process consumes area as well as power.
The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.